One of the applications of computerized object tracking is controlling people and object movement through a gate into and out of a restricted area enclosed by the gate. Conventionally, gate sensors are using optical devices ranging from simple non invisible infrared beams to video cameras directed to the gate area combined with image processors. Other conventional access control system of a gate use radio frequency identification (RFID) technology to detect movement of vehicles or people through a gate. RFID Systems consist of a transponder (tag), which is a microchip connected to an antenna. The tag affixed to an item is communicating with a reader device via radio waves. Depending on the type of tag used, the reader can receive detailed information or can receive data as simple as an identification number. The basic types of RFID tags can be classified as read/write and read only. The data stored on read/write tags can be edited, added to, or completely rewritten, when the tag is within the range of a reader. Data stored on a read only tag can be read, but cannot be edited in any way. In a gate sensor application, an RFID reader is disposed at the gate and objects like vehicles have RFID tags attached to them. When the vehicle passes through the gate, the gate RFID reader identifies the crossing vehicle by communicating with the RFID tag. RFID tags are used for example for automatically charging car drivers passing through highway toll booths. An RFID reader mounted on a toll gate identifies RFID tagged cars crossing the toll gate at high speed, by receiving identification data from their tags. The gate RFID readers are linked through a communication network to a central controller.
In a number of applications, conventional gate sensors face complicated and challenging operational conditions. A vehicle, for example, may stop at the gate area, maneuver in the area close to the gate and change direction of movement near the gate area. A conventional optical or RFID gate detector may give a false detection of gate crossing under this condition. The various modes of motion through a gate entails that a reliable detection of gate crossing of a gate sensor has can become a non trivial problem. Furthermore, gate crossing can be distributed at unattended remote sites that do not provide service and support means for a gate crossing detector.
U.S. Pat. No. 5,661,457 (Ghaffari et al.), which is discussed here for reference, discloses a directional antenna configuration for use in an article tracking system that includes two shorted loops, one on each side of a portal and in each case circumscribing the portal. The antenna configuration also includes a respective pair of passage antennas provided on each side of the portal. The passage antennas are all arranged in planes parallel to the path of travel through the doorway. The respective loops confine the effective detection areas of each pair of passage antennas to the respective side of the portal. The antenna configuration permits reliable detection of direction of movement through the portal. Gate crossing detection disclosed in this invention provides improved moving direction capability, however, the system configuration, whereas the detector is connected to a central unit, is adaptable to detection of crossing gates to enclosed areas does not address the broader issue of zone crossing in remote unattended areas.
Thus there is long felt need for a gate crossing detector, capable of adequately and reliably determine gate crossing and direction gate crossing with an extended capability detection of line crossing in unattended remote areas.